Manipulating hydrophilicity of conventional dye molecules for tracer applications

ABSTRACT

A composition includes a functionalized fluorescent dye. The functionalized fluorescent dye includes an isothiocyanate-containing dye that is functionalized with a functional group. The functional group includes a primary amine. The functionalized fluorescent dye can be mixed with a fluid to form a tracer fluid for tracing fluid flow in a subterranean formation.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional of and claims the benefit of priorityto U.S. patent application Ser. No. 17/548,837, filed Dec. 13, 2021, thecontents of which are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to methods and compositions used in generatingand using functionalized fluorescent tracers in drilling and oil wellapplications.

BACKGROUND

Tracer techniques can be a powerful diagnostic tool in numerousscientific disciplines and for technologies in many industrial sectors.Molecular tracers can include water-soluble or oil-soluble compounds. Infield tests of oilfields, water-soluble tracers can provide a betterunderstanding of the studied oil reservoir, for example, a betterunderstanding of inter-well connections, connections between layers andheterogeneities. Similarly, oil-soluble tracers can provide informationon petroleum products, for example qualitative analysis of theproduction fluid return from multiple stage completions, either verticalor horizontal completions.

SUMMARY

This disclosure describes technologies relating to functionalizedfluorescent tracers, methods of making the tracers, and methods of usingthe tracers. Certain aspects of the subject matter described can beimplemented as a composition. The composition includes a functionalizedfluorescent dye. The functionalized fluorescent dye includes anisothiocyanate-containing dye that is functionalized with a functionalgroup. The functional group includes a primary amine. Theisothiocyanate-containing dye is selected from the group consisting offluorescein isothiocyanate, Rhodamine B isothiocyanate, ortetramethylrhodamine isothiocyanate, or any isoform thereof. Thefunctional group is selected from Group I or Group II. Group I consistsof aminomethanesulfonic acid, 2-aminoethanesulfonic acid,3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and3-aminopropyl(trimethyl)azanium. Group II consists of4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid,2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid,4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium,6-amino-4-hydroxy-2-naphthalenesulfonic acid,1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonicacid, 4-aminonaphthalene-1,7-disulfonic acid,8-amino-1,3,6-naphthalenetrisulfonic acid, and8-aminopyrene-1,3,6-trisulfonic acid.

This, and other aspects, can include one or more of the followingfeatures. In some implementations, the isothiocyanate-containing dye isRhodamine B isothiocyanate, and the functional group is4-aminobenzenesulfonic acid. In some implementations, theisothiocyanate-containing dye is fluorescein isothiocyanate, and thefunctional group is 2-aminoethyl(trimethyl)azanium. In someimplementations, the isothiocyanate-containing dye istetramethylrhodamine isothiocyanate, and the functional group is2-aminoethanesulfonic acid.

Certain aspects of the subject matter described can be implemented as amethod of making a functionalized fluorescent dye. A water-solubleisothiocyanate-containing fluorescent dye is dissolved in an aqueoussolvent to yield an aqueous dye solution. The water-solutbleisothiocyanate-containing fluorescent dye is selected from the groupconsisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, ortetramethylrhodamine isothiocyanate, or any isoform thereof. Afunctional group is dissolved in water to yield an aqueous functionalgroup solution. The functional group includes a primary amine. Thefunctional group is selected from Group I or Group II. Group I consistsof aminomethanesulfonic acid, 2-aminoethanesulfonic acid,3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and3-aminopropyl(trimethyl)azanium. Group II consists of4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid,2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid,4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium,6-amino-4-hydroxy-2-naphthalenesulfonic acid,1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonicacid, 4-aminonaphthalene-1,7-disulfonic acid,8-amino-1,3,6-naphthalenetrisulfonic acid, and8-aminopyrene-1,3,6-trisulfonic acid. The aqueous dye solution and theaqueous functional group solution are mixed to form the functionalizedfluorescent dye. The functionalized fluorescent dye is a reactionproduct of the water-soluble isothiocyanate-containing dye and thefunctional group.

This, and other aspects, can include one or more of the followingfeatures. The aqueous solvent can be a mixture of water and ethanol. Insome implementations, a volumetric ratio of water to ethanol of theaqueous solvent is in a range of from 1:1 to 9:1. In someimplementations, the water is deionized water.

Certain aspects of the subject matter described can be implemented as amethod. A functionalized fluorescent tracer and a fluid are mixed toform a tracer fluid. The functionalized fluorescent tracer includes anisothiocyanate-containing dye that is functionalized with a functionalgroup. The functional group includes a primary amine. Theisothiocyanate-containing dye is selected from the group consisting offluorescein isothiocyanate, Rhodamine B isothiocyanate, ortetramethylrhodamine isothiocyanate, or any isoform thereof. Thefunctional group is selected from Group I or Group II. Group I consistsof aminomethanesulfonic acid, 2-aminoethanesulfonic acid,3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and3-aminopropyl(trimethyl)azanium. Group II consists of4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid,2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid,4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium,6-amino-4-hydroxy-2-naphthalenesulfonic acid,1-amino-2-naphthol-4-sulfonic acid, 7-aminonaphthalene-1,3-disulfonicacid, 4-aminonaphthalene-1,7-disulfonic acid,8-amino-1,3,6-naphthalenetrisulfonic acid, and8-aminopyrene-1,3,6-trisulfonic acid. The tracer fluid is flowed into afirst subterranean formation. A sample is recovered from the firstsubterranean formation or a second subterranean formation that isconnected to the first subterranean formation. The sample is analyzedfor a fluorescent signal.

This, and other aspects, can include one or more of the followingfeatures. The functionalized fluorescent tracer can be identified in thesample using fluorescence (for example, fluorescence imaging orfluorescence spectroscopy), ultraviolet-visible (UV-Vis) spectroscopy,Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, massspectroscopy (MS), high performance liquid chromatography (HPLC), liquidchromatography-mass spectroscopy (LC-MS), or pyrolysis gaschromatography-mass spectroscopy (pyrolysis GC-MS), or any combinationthereof. The sample can be a fluid sample, a solid sample, or a samplethat includes both fluid and solid. The fluid (mixed with thefunctionalized fluorescent tracer) can be a fracking fluid or a drillingmud.

The details of one or more implementations of the subject matter of thisdisclosure are set forth in the accompanying drawings and thedescription. Other features, aspects, and advantages of the subjectmatter will become apparent from the description, the drawings, and theclaims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an example well.

FIG. 2 is a flow chart of an example method for making a functionalizedfluorescent dye that can be used in the well of FIG. 1 .

FIG. 3 is a flow chart of an example method for treating a well.

FIG. 4 is a molecular structure of an example functionalized fluorescentdye.

FIG. 5 is a molecular structure of an example functionalized fluorescentdye.

FIG. 6 is a molecular structure of an example functionalized fluorescentdye.

DETAILED DESCRIPTION

This disclosure describes functionalized fluorescent tracers, methods ofmaking the tracers, and methods of using the tracers. The functionalizedfluorescent tracers can be used, for example, to track aqueous fluids inwells. A chemical method can be implemented to modify the structures ofconventional fluorescent dye molecules by covalently bonding ahydrophilic functional group to the dye molecule, which can increase thefluorescent dye's hydrophilicity. The resulting dye exhibits enhancedsolubility in water while retaining its fluorescence. The hydrophilicfunctional group can also serve as a molecular identifier.

FIG. 1 depicts an example of a drilling operation 10 for a well 12. Thewell 12 can be in a wellbore 20 formed in a subterranean zone 14 of ageological formation in the Earth's crust. The well 12 enables access tothe subterranean zone 14 to allow recovery (that is, production) offluids to the surface and, in some implementations, additionally oralternatively allows fluids to be placed in the Earth. The subterraneanzone 14 can include, for example, a formation, a portion of a formation,or multiple formations in a hydrocarbon-bearing reservoir from whichrecovery operations can be practiced to recover trapped hydrocarbons.Examples of unconventional reservoirs include tight-gas sands, gas andoil shales, coalbed methane, heavy oil and tar sands, gas-hydratedeposits, to name a few. In some implementations, the subterranean zone14 includes an underground formation including natural fractures 60 inrock formations containing hydrocarbons (for example, oil, gas, orboth). For example, the subterranean zone 14 can include a fracturedshale. In some implementations, the well 12 can intersect other suitabletypes of formations, including reservoirs that are not naturallyfractured.

The well 12 can include a casing 22 and well head 24. The wellbore 20can be a vertical, horizontal, deviated, or multilateral bore. Thecasing 22 can be cemented or otherwise suitably secured in the wellbore20. Perforations 26 can be formed in the casing 22 at the level of thesubterranean zone 14 to allow oil, gas, and by-products to flow into thewell 12 and be produced to the surface 25. Perforations 26 can be formedusing shape charges, a perforating gun, or otherwise.

For a drilling treatment 10, a work string 30 can be disposed in thewellbore 20. The work string 30 can be coiled tubing, sectioned pipe, orother suitable tubing. A drilling tool or drill bit 32 can be coupled toan end of the work string 30. Packers 36 can seal an annulus 38 of thewellbore 20 uphole of and downhole of the subterranean zone 14. Packers36 can be mechanical, fluid inflatable, or other suitable packers.

One or more pump trucks 40 can be coupled to the work string 30 at thesurface 25. The pump trucks 40 pump drilling mud 58 down the work string30 to lubricate and cool the drilling tool or drill bit 32, maintainhydrostatic pressure in the wellbore, and carry subterranean cuttings tothe surface. The drilling mud 58 can include a fluid pad, proppants,flush fluid, or a combination of these components. The pump trucks 40can include mobile vehicles, equipment such as skids, or other suitablestructures.

One or more instrument trucks 44 can also be provided at the surface 25.The instrument truck 44 can include a drilling control system 46 and adrilling simulator 47. The drilling control system 46 monitors andcontrols the drilling treatment 10. The drilling control system 46 cancontrol the pump trucks 40 and fluid valves to stop and start thedrilling treatment 10. The drilling control system 46 communicates withsurface and subsurface instruments to monitor and control the drillingtreatment 10. In some implementations, the surface and subsurfaceinstruments may comprise surface sensors 48, down-hole sensors 50, andpump controls 52.

Additives 81 can be mixed with drilling mud 58 or other drilling fluidsand flowed through the reservoir. In some implementations, the additives81 can include one or more tracers, for example, a fluorescent dye.Fluorescent dyes can be used as water-soluble tracers. These dyes areinexpensive and easy to use. Examples of fluorescent dyes includefluorescein, eosin, Rhodamine, and Rhodamine-B. However, these organicdye-based tracers have some shortcomings, and in particular, in relationfor use as water tracers. For example, the water-soluble tracersfluorescein, eosin, and Rhodamine can adsorb onto reservoir rock orpartially dissolve in the oil phase. In addition, the number of tracersis limited to the number of organic dye molecules available.

The tracers described herein overcome these shortcomings. These tracerscan be generated using a synthetic method to tune thehydrophilicity/hydrophobicity of water-soluble dye molecules bychemically modifying the molecular structure of the molecule. Forexample, by covalently grafting functional groups onto the dyemolecules, the various functional groups can create barcoded structuralinformation, resulting in new compounds. In some embodiments, byintroducing hydrophilic functional groups into water-soluble dyemolecules, the hydrophilicity of the resulting molecules can beenhanced, thus improving their solubility in an aqueous phase. Bytailoring the molecules, the hydrophilicity and hydrophobicity of themolecule can be adjusted to a desired degree. Therefore, the partitionof the molecule in an oil phase is controllable. This, in part, enablesthe potential application of these functionalized fluorescent dyes aspartition tracers for oil reservoir applications. The structure-modifieddyes reserve their fluorescence properties, although in someimplementations the fluorescence features may also be modified by theintroduction of functional groups. In some implementations, ahydrophilic functional group including a sulfonate anion or a quaternaryammonium cation can be introduced, resulting in dye compounds with lowsorption on rock in fluids. Sulfonate anions and quaternary ammoniumcations are highly hydrophilic and therefore highly soluble in water.Covalently bonding a functional group that includes one of these ions tothe fluorescent dye can enhance the dye's solubility in water.

These functionalized fluorescent dyes are described herein as barcodedor having barcode information. In this context, “barcode” refers to thefact that these functionalized dyes or tracers are uniquely identifiabletwo or more orthogonal analyses. As a first factor, the tracers can beidentified by their fluorescence signal, for example, by the wavelengthof the emission spectrum or simply by the presence of a fluorescentsignal. As a second factor, the tracers can be identified by their massor hydrophilicity. Accordingly, the unique combinations of the differentfluorophores and the different functionalization groups results in alibrary of barcoded tracers.

Barcoded tracers have several advantages. For example, differentcombinations of different tracers can be used simultaneously or inparallel to provide information about drilling operations orsubterranean formations. For example, two or more uniquely identifiabletracers can be injected at two or more different drilling sites and canyield information about inter well connectivity. In another example,uniquely identifiable tracers can be injected at the same drilling siteat different times, can yield temporal information about transit time,depth, or length of subterranean fractures or formations.

Further, the two-factor nature of the barcode tracers allows for anadvantageous two-factor analysis. The first factor, the fluorescencesignal, can be detected in an initial, rapid analysis. Accordingly,samples recovered from a drilling operation or subterranean formationcan be quickly and qualitative analyzed for the presence of afluorescence signal, i.e., a ‘yes/no’ analysis. In some implementations,this first analysis can be done on-site, and samples exhibiting afluorescence signal can be allocated for further processing. Next, thesamples exhibiting a fluorescence signal can be subsequently separatedand analyzed by mass or chromatographic methods, for example by highperformance liquid chromatography (HPLC), mass spectrometry (MS), orliquid chromatography—mass spectrometry (LC-MS) analysis.

A chemical method to modify the structures of conventional dye moleculesby introducing molecular barcode information and by tailoring thehydrophilicity and/or hydrophobicity of the conventional water-solubledye molecules is described herein. The resulting compounds expand thenumber of dyes available for tracer applications as water-solubletracers or partition tracers.

The new dye molecules include the general structure R_(I)—X—R_(II),where R_(I) is a fluorescent fluorophore. The fluorophore can be eitherhydrophilic or hydrophobic, and can be detectable by optical methods,for example, florescence imaging or molecular spectroscopy (absorbanceor fluorescence). In the general structure, X can be a linking molecule.X can be selected from the group that includes C₁₋₁₈ alkylene, C₁₋₁₈alkenylene, or C₁₋₁₈ alkynylene, where each of C₁₋₁₈ alkylene, C₁₋₁₈alkenylene, or C₁₋₁₈ alkynylene can be optionally replaced orinterrupted by any one of oxygen (O), sulfur (S), or an amine (NH). Insome implementations, X is a thiourea. In the general structure, R_(II)can be selected from the group that includes hydrogen, alkoxy,haloalkoxy (including Cl, Br, or I), aryl, or heteroaryl (including N,NH, O, or S). The Ru confers a molecular fingerprint or barcodestructure into the new compounds. The R_(I)—X—R_(II) compounds aredetectable by spectroscopy and imaging methods, for example, UV-Visiblespectroscopy (UV-Vis), fluorescence (such as fluorescence spectroscopyor fluorescence imaging), Fourier-transform infrared spectroscopy(FTIR), Raman spectroscopy, mass spectroscopy, or chromatography (suchas HPLC, LC-MS, or pyrolysis GC-MS).

In some implementations, the fluorescent dye R_(I) is fluoresceinisothiocyanate (FITC), Rhodamine B isothiocyanate (RBITC),tetramethylrhodamine isothiocyanate (MRITC or TRITC),1,1′-bis(3-isothiocyanatopropyl)-11-chloro-4,5:4′,5′-dibenzo-3,3,3′,3′-tetramethyl-10,12-trimethylenindotricarbocyaninebromide (NIR 5e), eosin-5-isothiocyanate, or any isomer thereof. Thestructures of FITC, RBITC, and MRITC/TRITC are shown in Table 1. Thesedyes are highly water-soluble, i.e., hydrophilic, and have fluorescenceemissions in the visible light spectral region. The excitation andemission wavelengths (in nanometers, nm) of these dyes are listed inTable 1.

TABLE 1 Water-Soluble Dyes and their Molecular Structure FluorescenceCAS Dye compound Molecular structure; Molecular weightλ_(excitation)/λ_(emission) Number/Isomers Fluorescein isothiocyanate(FITC)

495 nm/519 nm 27072-45-3 (mixed isomers); 3326-32-7 (5-isomer);18861-78-4 (6-isomer) Rhodamine B isothiocyanate (RBITC)

570 nm/595 nm 36877-69-7 (mixed isomers) Tetramethylrhodamineisothiocyanate (MRITC or TRITC)

544 nm/570 nm 95197-95-8 (mixed isomers); 80724-20-5 (Isomer R);80724-19-2 (5-TRITC)

The dyes shown in Table 1 were each modified with additional functionalgroups. The functional groups are added using the reaction of a primaryamine with an isothiocyanate to result in a substituted thiourea, asshown in Equation 1.

R_(II) is a hydrophilic functional group that includes a primary aminegroup and a sulfonate anion (or sulfonic acid) or a quaternary ammoniumcation, or other suitable amine-containing hydrophilic functional group,and R_(I) is the isothiocyanate-containing fluorescent dye, where inEquation 1 the isothiocyanate group is expanded for clarity.

FIG. 2 is a flow chart of an example method 200 of making afunctionalized fluorescent dye. The reactions were performed at roomtemperature in a bi-phase system. At block 202, a water-solubleisothiocyanate-containing fluorescent dye (such as FITC, RBITC, MRITC,or TRITC) is dissolved in an aqueous solvent to yield an aqueous dyesolution. In some implementations, the aqueous dye solution at block 202is deionized water. In some implementations, the aqueous dye solution atblock 202 is a mixture of water and ethanol. For example, the aqueousdye solution at block 202 can be a water/ethanol mixture with a 9:1volumetric ratio of water to ethanol. For example, the aqueous dyesolution at block 202 can be a water/ethanol mixture with a 1:1volumetric ratio of water to ethanol. At block 204, a functional groupis dissolved in water to yield an aqueous functional group solution. Forexample, the functional group is dissolved in deionized water at block204. The functional group at block 204 is hydrophilic and includes aprimary amino group (amine compound). In some implementations, the aminecompound at block 204 includes a hydrocarbon chain (examples areprovided in Table 2) or an aromatic portion (examples are provided inTable 3). In some implementations, the amine compound at block 204includes a sulfonate anion (or sulfonic acid) or a quaternary ammoniumcation (examples are provided in both Table 2 and Table 3). The aqueousdye solution and the aqueous functional group solution each contain thesame molecular molar concentration of fluorescent dye and the aminecompound, respectively. At block 206, the aqueous dye solution and theaqueous functional group solution are mixed to form the functionalizedfluorescent dye. In some implementations, the aqueous dye solution andthe aqueous functional group solution are mixed in equal volumes atblock 206 and stirred vigorously. In some implementations, the reactionbetween the fluorescent dye and the functional group is allowed tocontinue under stirring for at least 12 hours at block 206. Thefunctionalized fluorescent dye formed at block 206 is a reaction productof the water-soluble isothiocyanate-containing dye and the amine-groupcontaining hydrophilic functional group.

Tables 2 and 3 illustrate different amine-containing functional groupsthat can be used to functionalize an isothiocyanate dye. The compoundsshown in Table 2 are nonaromatic compounds with primary amino groups andeither a sulfonate anion (or sulfonic acid) or a quaternary ammoniumcation. The compounds have different molecular weights and provide bothbarcode information and the ability to tailor the hydrophilicity andmiscibility with water of the resulting compound, based on, for example,alkyl chain length. Accordingly, isothiocyanate dyes functionalized withthe compounds listed in Table 2 can have variable partitioning in oilphases.

The compounds shown in Table 3 are aromatic compounds with primary aminogroups and either a sulfonate anion (or sulfonic acid) or a quaternaryammonium cation. The compounds have different molecular weights andprovide both barcode information and the ability to tailor thehydrophilicity and miscibility with water of the resulting compound,based on, for example, the number of cyclic rings and/or the number ofsulfonate anions. Accordingly, isothiocyanate dyes functionalized withthe compounds listed in Table 2 can have variable partitioning in oilphases.

TABLE 2 Nonaromatic Compounds with Primary Amino Groups MolecularStructure/Weight Compound (Daltons) CAS number Aminomethane- sulfonicacid

13881-91-9 2-aminoethane- sulfonic acid

107-35-7 3-amino-1- propanesulfonic acid

3687-18-1 2-aminoethyl (trimethyl) azanium

38170-37-5 3-aminopropyl (trimethyl) azanium

58999-88-5

TABLE 3 Aromatic Compounds with Primary Amino Groups Compound MolecularStructure/Weight (Daltons) CAS number 4-aminobenzenesulfonic acid

121-57-3 3-aminobenzenesulfonic acid

121-47-1 2-aminobenzenesulfonic acid

88-21-1 3-amino-4-hydroxybenzenesulfonic acid

98-37-3 4-amino-3-hydroxybenzenesulfonic acid

2592-14-5 (4-aminophenyl)-trimethylazanium

21248-43-1 6-amino-4-hydroxy-2-naphthalenesulfonic acid

90-51-7 4-amino-3-hydroxy-1-naphthalenesulfonic acid

116-63-2 7-aminonaphthalene-1,3-disulfonic acid

86-65-7 4-aminonaphthalene-1,7-disulfonic acid

85-74-5 8-amino-1,3,6-naphthalenetrisulfonic acid

117-42-0 8-aminopyrene-1,3,6-trisulfonic acid

51987-58-7

The dyes described herein can be used as water tracers in subterraneanapplications. For example, multistage hydraulic fracturing along ahorizontal well is key to effectively recover hydrocarbons from tightreservoirs. Improving the hydrocarbon recovery requires detailedproduction information of each hydraulic fracture. Water-solublechemical tracers are often used to calculate the production profile frommultistage fracturing through a tracer flow back test. Further, thesesynthesized barcoded water-soluble compounds can also be added to mudformulations in water-based drilling fluids as mud tracers for mudlogging applications.

With the barcoded water-soluble tracers described herein, qualitativeanalysis by fluorescence spectroscopy or imaging can be used for watertracing applications, for example, in single or inter-well test waterflooding or in hydraulic fracturing, while detailed molecular barcodeinformation can be revealed by HPLC, LC-MS, or pyrolysis GC-MS analysisto identify each tracer from different locations.

FIG. 3 is a flow chart of an example method 300 of tracing fluid flow ina subterranean formation. At block 302, a functionalized fluorescenttracer and a fluid are mixed to form a tracer fluid. At block 304, thetracer fluid is flowed into a first subterranean formation. At block306, a sample is recovered from the first subterranean formation or asecond subterranean formation connected to the first subterraneanformation. At block 308, the sample is analyzed for a fluorescentsignal. At block 310, the sample is further separated and analyzed for abarcode functional group. For example, the sample is analyzed at block310 to identify the barcode functional group present in thefunctionalized fluorescent tracer.

Example 1

34.6 milligrams (mg) of 4-aminobenzenesulfonic acid was dissolved in 25milliliters (mL) of deionized water, and 0.5 mL of ammonia water(NH₃·H₂O, 29.5 weight percent) was added to adjust the pH of thesolution to about 9. 53.6 mg of RBITC was dissolved in 25 mL of awater/ethanol mixture with a 9:1 volumetric ratio of water to ethanol.The two solutions were mixed and reacted for more than 12 hours undervigorous stirring at room temperature. The molecular structure of thefunctionalized fluorescent dye is shown in FIG. 4 .

Example 2

35 mg of (2-aminoethyl)trimethylammonium chloride hydrochloride wasdissolved in 25 mL of deionized water. 38.9 mg of FITC was dissolved in25 mL of a water/ethanol mixture with a 1:1 volumetric ratio of water toethanol. The two solutions were mixed and reacted for more than 12 hoursunder vigorous stirring at room temperature. The molecular structure ofthe functionalized fluorescent dye is shown in FIG. 5 .

Example 3

25 mg of 2-aminoethanesulfonic acid was dissolved in 25 mL of deionizedwater, and 0.5 mL of ammonia water (NH₃·H₂O, 29.5 weight percent) wasadded to adjust the pH of the solution to about 9. 44.4 mg of TRITC wasdissolved in 25 mL of a water/ethanol mixture with a 9:1 volumetricratio of water to ethanol. The two solutions were mixed and reacted formore than 12 hours under vigorous stirring at room temperature. Themolecular structure of the functionalized fluorescent dye is shown inFIG. 6 .

Examples 1, 2, and 3 provide example procedures for making afunctionalized fluorescent dye. With similar procedures, any one of theorganic, fluorescent dyes shown in Table 1 can be combined with any oneof the nonaromatic functional groups containing primary amino groupsshown in Table 2 or any one of the aromatic functional groups containingprimary amino groups shown in Table 3. The following includes examplecombinations of organic, fluorescent dyes and functional groups that canbe combined to make a functionalized fluorescent dye. FITC andaminomethanesulfonic acid can be combined to make a functionalizedfluorescent dye. FITC and 2-aminoethanesulfonic acid can be combined tomake a functionalized fluorescent dye. FITC and3-amino-1-propanesulfonic acid can be combined to make a functionalizedfluorescent dye. FITC and 3-aminopropyl(trimethyl)azanium can becombined to make a functionalized fluorescent dye. FITC and4-aminobenzenesulfonic acid can be combined to make a functionalizedfluorescent dye. FITC and 3-aminobenzenesulfonic acid can be combined tomake a functionalized fluorescent dye. FITC and 2-aminobenzenesulfonicacid can be combined to make a functionalized fluorescent dye. FITC and3-amino-4-hydroxybenzenesulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and4-amino-3-hydroxybenzenesulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and(4-aminophenyl)-trimethylazanium can be combined to make afunctionalized fluorescent dye. FITC and6-amino-4-hydroxy-2-naphthalenesulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and4-amino-3-hydroxy-1-naphthalenesulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and7-aminonaphthalene-1,3-disulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and4-aminonaphthalene-1,7-disulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and8-amino-1,3,6-naphthalenetrisulfonic acid can be combined to make afunctionalized fluorescent dye. FITC and 8-aminopyrene-1,3,6-trisulfonicacid can be combined to make a functionalized fluorescent dye. RBITC andaminomethanesulfonic acid can be combined to make a functionalizedfluorescent dye. RBITC and 2-aminoethanesulfonic acid can be combined tomake a functionalized fluorescent dye. RBITC and3-amino-1-propanesulfonic acid can be combined to make a functionalizedfluorescent dye. RBITC and 2-aminoethyl(trimethyl)azanium can becombined to make a functionalized fluorescent dye. RBITC and3-aminopropyl(trimethyl)azanium can be combined to make a functionalizedfluorescent dye. RBITC and 3-aminobenzenesulfonic acid can be combinedto make a functionalized fluorescent dye. RBITC and2-aminobenzenesulfonic acid can be combined to make a functionalizedfluorescent dye. RBITC and 3-amino-4-hydroxybenzenesulfonic acid can becombined to make a functionalized fluorescent dye. RBITC and4-amino-3-hydroxybenzenesulfonic acid can be combined to make afunctionalized fluorescent dye. RBITC and(4-aminophenyl)-trimethylazanium can be combined to make afunctionalized fluorescent dye. RBITC and6-amino-4-hydroxy-2-naphthalenesulfonic acid can be combined to make afunctionalized fluorescent dye. RBITC and4-amino-3-hydroxy-1-naphthalenesulfonic acid can be combined to make afunctionalized fluorescent dye. RBITC and7-aminonaphthalene-1,3-disulfonic acid can be combined to make afunctionalized fluorescent dye. RBITC and4-aminonaphthalene-1,7-disulfonic acid can be combined to make afunctionalized fluorescent dye. RBITC and8-amino-1,3,6-naphthalenetrisulfonic acid can be combined to make afunctionalized fluorescent dye. RBITC and8-aminopyrene-1,3,6-trisulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and aminomethanesulfonic acid canbe combined to make a functionalized fluorescent dye. TRITC and3-amino-1-propanesulfonic acid can be combined to make a functionalizedfluorescent dye. TRITC and 2-aminoethyl(trimethyl)azanium can becombined to make a functionalized fluorescent dye. TRITC and3-aminopropyl(trimethyl)azanium can be combined to make a functionalizedfluorescent dye. TRITC and 4-aminobenzenesulfonic acid can be combinedto make a functionalized fluorescent dye. TRITC and3-aminobenzenesulfonic acid can be combined to make a functionalizedfluorescent dye. TRITC and 2-aminobenzenesulfonic acid can be combinedto make a functionalized fluorescent dye. TRITC and3-amino-4-hydroxybenzenesulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and4-amino-3-hydroxybenzenesulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and(4-aminophenyl)-trimethylazanium can be combined to make afunctionalized fluorescent dye. TRITC and6-amino-4-hydroxy-2-naphthalenesulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and4-amino-3-hydroxy-1-naphthalenesulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and7-aminonaphthalene-1,3-disulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and4-aminonaphthalene-1,7-disulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and8-amino-1,3,6-naphthalenetrisulfonic acid can be combined to make afunctionalized fluorescent dye. TRITC and8-aminopyrene-1,3,6-trisulfonic acid can be combined to make afunctionalized fluorescent dye.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of what may beclaimed, but rather as descriptions of features that may be specific toparticular implementations. Certain features that are described in thisspecification in the context of separate implementations can also beimplemented, in combination, in a single implementation. Conversely,various features that are described in the context of a singleimplementation can also be implemented in multiple implementations,separately, or in any sub-combination. Moreover, although previouslydescribed features may be described as acting in certain combinationsand even initially claimed as such, one or more features from a claimedcombination can, in some cases, be excised from the combination, and theclaimed combination may be directed to a sub-combination or variation ofa sub-combination.

As used in this disclosure, the terms “a,” “an,” or “the” are used toinclude one or more than one unless the context clearly dictatesotherwise. The term “or” is used to refer to a nonexclusive “or” unlessotherwise indicated. The statement “at least one of A and B” has thesame meaning as “A, B, or A and B.” In addition, it is to be understoodthat the phraseology or terminology employed in this disclosure, and nototherwise defined, is for the purpose of description only and not oflimitation. Any use of section headings is intended to aid reading ofthe document and is not to be interpreted as limiting; information thatis relevant to a section heading may occur within or outside of thatparticular section.

As used in this disclosure, the term “about” or “approximately” canallow for a degree of variability in a value or range, for example,within 10%, within 5%, or within 1% of a stated value or of a statedlimit of a range.

As used in this disclosure, the term “substantially” refers to amajority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%,95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999%or more.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited. For example, arange of “0.1% to about 5%” or “0.1% to 5%” should be interpreted toinclude about 0.1% to about 5%, as well as the individual values (forexample, 1%, 2%, 3%, and 4%) and the sub-ranges (for example, 0.1% to0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. Thestatement “X to Y” has the same meaning as “about X to about Y,” unlessindicated otherwise. Likewise, the statement “X, Y, or Z” has the samemeaning as “about X, about Y, or about Z,” unless indicated otherwise.

The term “downhole” as used in this disclosure refers to under thesurface of the earth, such as a location within or fluidly connected toa wellbore.

As used in this disclosure, the term “drilling fluid” refers to fluids,slurries, or muds used in drilling operations downhole, such as duringthe formation of the wellbore.

As used in this disclosure, the term “fluid” refers to gases, liquids,gels, and any combination of these, unless otherwise indicated.

As used in this disclosure, the term “subterranean material” or“subterranean zone” or “subterranean formation” refers to any materialunder the surface of the earth, including under the surface of thebottom of the ocean. For example, a subterranean zone or material can beany section of a wellbore and any section of a subterranean petroleum-or water-producing formation or region in fluid contact with thewellbore. Placing a material in a subterranean zone can includecontacting the material with any section of a wellbore or with anysubterranean region in fluid contact the material. Subterraneanmaterials can include any materials placed into the wellbore such ascement, drill shafts, liners, tubing, casing, or screens; placing amaterial in a subterranean zone can include contacting with suchsubterranean materials. In some examples, a subterranean zone ormaterial can be any downhole region that can produce liquid and/orgaseous petroleum materials, water, or any downhole section in fluidcontact with liquid or gaseous petroleum materials, or water. Forexample, a subterranean zone or material can be at least one of an areadesired to be fractured, a fracture or an area surrounding a fracture,and a flow pathway or an area surrounding a flow pathway, in which afracture or a flow pathway can be optionally fluidly connected to asubterranean petroleum- or water-producing region, directly or throughone or more fractures or flow pathways.

As used in this disclosure, “treatment of a subterranean zone” caninclude any activity directed to extraction of water or petroleummaterials from a subterranean petroleum- or water-producing formation orregion, for example, including drilling, stimulation, hydraulicfracturing, clean-up, acidizing, completion, cementing, remedialtreatment, abandonment, aquifer remediation, identifying oil richregions via imaging techniques, and the like.

As used in this disclosure, a “flow pathway” downhole can include anysuitable subterranean flow pathway through which two subterraneanlocations are in fluid connection. The flow pathway can be sufficientfor petroleum and/or water to flow from one subterranean location to thewellbore or vice-versa. A flow pathway can include at least one of ahydraulic fracture, and a fluid connection across a screen, acrossgravel pack, across proppant, including across resin-bonded proppant orproppant deposited in a fracture, and across sand. A flow pathway caninclude a natural subterranean passageway through which fluids can flow.In some implementations, a flow pathway can be a water source and caninclude water. In some implementations, a flow pathway can be apetroleum source and can include petroleum. In some implementations, aflow pathway can be sufficient to divert water, a downhole fluid, or aproduced hydrocarbon from a wellbore, fracture, or flow pathwayconnected to the pathway.

As used in this disclosure, “weight percent” (wt. %) can be considered amass fraction or a mass ratio of a substance to the total mixture orcomposition. Weight percent can be a weight-to-weight ratio ormass-to-mass ratio, unless indicated otherwise.

Particular implementations of the subject matter have been described.Other implementations, alterations, and permutations of the describedimplementations are within the scope of the following claims as will beapparent to those skilled in the art. While operations are depicted inthe drawings or claims in a particular order, this should not beunderstood as requiring that such operations be performed in theparticular order shown or in sequential order, or that all illustratedoperations be performed (some operations may be considered optional), toachieve desirable results. In certain circumstances, multitasking orparallel processing (or a combination of multitasking and parallelprocessing) may be advantageous and performed as deemed appropriate.

Moreover, the separation or integration of various system modules andcomponents in the previously described implementations should not beunderstood as requiring such separation or integration in allimplementations, and it should be understood that the describedcomponents and systems can generally be integrated together or packagedinto multiple products.

Accordingly, the previously described example implementations do notdefine or constrain the present disclosure. Other changes,substitutions, and alterations are also possible without departing fromthe spirit and scope of the present disclosure.

What is claimed is:
 1. A method of making a functionalized fluorescentdye, comprising: dissolving a water-soluble isothiocyanate-containingfluorescent dye in an aqueous solvent to yield an aqueous dye solution,wherein the water-soluble isothiocyanate-containing fluorescent dye isselected from the group consisting of fluorescein isothiocyanate,Rhodamine B isothiocyanate, or tetramethylrhodamine isothiocyanate, orany isoform thereof; dissolving a functional group in water to yield anaqueous functional group solution, wherein the functional groupcomprises a primary amine and is selected from Group I or Group II,wherein: Group I consists of aminomethanesulfonic acid,2-aminoethanesulfonic acid, 3-amino-1-propanesulfonic acid,2-aminoethyl(trimethyl)azanium, and 3-aminopropyl(trimethyl)azanium; andGroup II consists of 4-aminobenzenesulfonic acid, 3-aminobenzenesulfonicacid, 2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonicacid, 4-amino-3-hydroxybenzenesulfonic acid,(4-aminophenyl)-trimethylazanium,6-amino-4-hydroxy-2-naphthalenesulfonic acid,4-amino-3-hydroxy-1-naphthalenesulfonic acid,7-aminonaphthalene-1,3-disulfonic acid,4-aminonaphthalene-1,7-disulfonic acid,8-amino-1,3,6-naphthalenetrisulfonic acid, and8-aminopyrene-1,3,6-trisulfonic acid; and mixing the aqueous dyesolution and the aqueous functional group solution to form thefunctionalized fluorescent dye, wherein the functionalized fluorescentdye is a reaction product of the water-soluble isothiocyanate-containingdye and the functional group.
 2. The method of claim 1, wherein theaqueous solvent is a mixture of water and ethanol.
 3. The method ofclaim 2, wherein a volumetric ratio of water to ethanol of the aqueoussolvent is in a range of from 1:1 to 9:1.
 4. The method of claim 1,wherein the water is deionized water.
 5. A method of tracing fluid flowin a subterranean formation, comprising: mixing a functionalizedfluorescent tracer and a fluid to yield a tracer fluid, wherein thefunctionalized fluorescent tracer comprises an isothiocyanate-containingdye functionalized with a functional group comprising a primary amine,wherein: the isothiocyanate-containing dye is selected from the groupconsisting of fluorescein isothiocyanate, Rhodamine B isothiocyanate, ortetramethylrhodamine isothiocyanate, or any isoform thereof; and thefunctional group is selected from Group I or Group II, wherein: Group Iconsists of aminomethanesulfonic acid, 2-aminoethanesulfonic acid,3-amino-1-propanesulfonic acid, 2-aminoethyl(trimethyl)azanium, and3-aminopropyl(trimethyl)azanium; and Group II consists of4-aminobenzenesulfonic acid, 3-aminobenzenesulfonic acid,2-aminobenzenesulfonic acid, 3-amino-4-hydroxybenzenesulfonic acid,4-amino-3-hydroxybenzenesulfonic acid, (4-aminophenyl)-trimethylazanium,6-amino-4-hydroxy-2-naphthalenesulfonic acid,4-amino-3-hydroxy-1-naphthalenesulfonic acid,7-aminonaphthalene-1,3-disulfonic acid,4-aminonaphthalene-1,7-disulfonic acid,8-amino-1,3,6-naphthalenetrisulfonic acid, and8-aminopyrene-1,3,6-trisulfonic acid; flowing the tracer fluid into afirst subterranean formation; recovering a sample from the firstsubterranean formation or a second subterranean formation connected tothe first subterranean formation; and analyzing the sample for afluorescent signal.
 6. The method of claim 5, comprising identifying thefunctionalized fluorescent tracer in the sample using fluorescenceimaging, fluorescence spectroscopy, ultraviolet-visible (UV-Vis)spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Ramanspectroscopy, mass spectroscopy (MS), high performance liquidchromatography (HPLC), liquid chromatography-mass spectroscopy (LC-MS),or pyrolysis gas chromatography-mass spectroscopy (pyrolysis GC-MS), orany combination thereof.
 7. The method of claim 5, where in the sampleis a fluid sample.
 8. The method of claim 5, wherein the fluid is afracking fluid.
 9. The method of claim 5, wherein the fluid is adrilling mud.